svn commit: r286374 - head/sys/x86/x86

[Konstantin Belousov]

Author: kib
Date: Thu Aug  6 18:02:54 2015
New Revision: 286374
URL: https://svnweb.freebsd.org/changeset/base/286374

Log:
  Formally pair store_rel(&smp_started) with load_acq(&smp_started).
  The expected semantic is to have misc. data, e.g. CPU bitmaps, visible
  in the BSP after smp_started is written by the last started AP, which
  formally requires acquire barrier on the load.  The change is mostly
  nop due to the ordered behaviour of the x86 CPUs.
  
  Reviewed by:	alc
  Sponsored by:	The FreeBSD Foundation
  MFC after:	2 weeks

Modified:
  head/sys/x86/x86/mp_x86.c

Modified: head/sys/x86/x86/mp_x86.c
==============================================================================
--- head/sys/x86/x86/mp_x86.c	Thu Aug  6 17:13:34 2015	(r286373)
+++ head/sys/x86/x86/mp_x86.c	Thu Aug  6 18:02:54 2015	(r286374)
@@ -602,7 +602,7 @@ init_secondary_tail(void)
 	mtx_unlock_spin(&ap_boot_mtx);
 
 	/* Wait until all the AP's are up. */
-	while (smp_started == 0)
+	while (atomic_load_acq_int(&smp_started) == 0)
 		ia32_pause();
 
 	/* Start per-CPU event timers. */